1. Field of the Invention
This invention relates to a soldering method and apparatus for electrically connecting parts loaded on a substrate to the substrate.
2. Description of the Related Art
On a substrate carrying a variety of circuits of an electronic equipment, such as a printed wired board, there are mounted electronic parts making up the circuits. These electronic parts are mounted by insertion, as in the case of lead parts, or by surface mounting, as in the case of chips. The electronic parts, so mounted, are electrically connected on the printed wired board by soldering. As soldering systems, there are a flow soldering system and a re-flow soldering system.
In the flow soldering system, a printed wired board is passed through a soldering vessel containing a fused solder. In the re-flow soldering system, cream solder, for example, is coated on a pre-set site of the printed wired board and, after mounting the chip, the soldering portion of the printed wired board is heated in a re-flow furnace.
Non-heat-resistant electronic parts, such as lead parts of transformers, variable resistor, air-core coil or a chemical capacitor, are soldered by flow soldering to the printed wired board, whereas heat-resistant electronic parts, such as chip parts of resistors, capacitors or IC packages, are soldered by re-flow soldering to the printed wired board.
Usually, the non-heat-resistant electronic parts, that is electronic parts that can be soldered by the flow soldering system, and the heat-resistant electronic parts, that cannot be soldered satisfactorily unless the re-flow soldering system is used, are soldered to a sole printed wired board to improve productivity as well as to achieve size reduction.
This applies when, for example, a tuner circuit for a high frequency portion of a TV receiver and an IF circuit are constructed on a sole printed wired board. It is therefore necessary to use the flow soldering system or a re-flow soldering system depending on the type of the electronic parts to be mounted on the sole printed wired board.
FIG. 1 shows a typical process for conventional re-flow soldering. Referring to FIG. 1A, on an upper surface 110 of a printed wired board P, there are already mounted chip parts 111, 112 as heat-resistant electronic parts, by re-flow soldering. First, to a lead land of the upper surface 110 of the printed wired board P, cream solder 121 is applied, using a multiple dispenser (nozzle). Then, as shown in FIG. 1Bm the printed wired board P is inverted upside down and lead parts 101, 102 and 103, as non-heat-resistant electronic parts, are mounted on the upper surface 100 of the printed wired board P.
The printed wired board P is then charged into the re-flow furnace and hot air is injected on to the lower surface 110, that is the part soldering surface, of the printed wired board P, as shown in FIG. 1D, to fuse the cream solder 121 under heating, at the same time as cold air is blown onto an upper surface 100, that is a part setting surface, to cool the lead parts 101 to 103. Then, cool air is blown onto the soldering surface 110, as shown in FIG. 1E, to cool and cure the cream solder 121 to solder respective connection terminals 120 of the lead parts 101 to 103.
However, in the above-described re-flow furnace, the part setting surface 100 is cooled by cool air during the solder fusing process (re-flow zone). So, the lead parts 101 to 103 are already cooled before start of the cooling process. Since only the part soldering surface 110 is cooled with cool air, remaining heat of the part soldering surface 110 is transmitted to the part setting surface 100, with the result that the lead parts 101 to 103 are heated abnormally as indicated in portion A of FIG. 2. So, the lead parts 101 to 103 as non-heat-resistant parts tend to be lowered in reliability.
There is also known a re-flow furnace having cooling means for efficiently cooling the non-heat-resistant parts loaded on the substrate to prevent the parts from being damaged by heat hysteresis by cooling the part setting surface 100 with a weak wind.
Meanwhile, the above-described re-flow furnace is constructed so that hot air for heating is ejected to a printed wired board P, transported by a conveyor 130, through an opening, not shown, provided in a re-flow panel 131 mounted facing the part setting surface 110 of the printed wired board P, as shown in FIG. 3A, onto the part setting surface 110 so as to be discharged via a vent port 132.
An upper portion of a rear area of the re-flow panel 131 not facing the printed wired board P, there is provided a cover 133 for shielding hot air from the opening of the re-flow panel 131 not contributing to the heating of the printed wired board P.
However, in the above-described soldering apparatus (re-flow furnace), part of hot air ejected via a hole in the re-flow panel 131, that is hot air from an area (unused portion) not facing the printed wire board P, is allowed to flow around the cover 133, without contributing to the heating of the printed wiring board P, and is then directed to the part setting setting surface 100 of the printed wiring board P. On the other hand, the forward side of the re-flow panel 131 not facing the printed wiring board P is devoid of the cover 133 so that it is always exposed to the ejected hot air. The result is that the non-heat-resistant parts on the side part setting surface is also heated by the hot air HW, as shown in FIG. 3B, to lower the part cooling effect, while the thermal energy is wasted to lower the heating efficiency by re-flow panel 131.
So, if a printed wired board is small in size but is loaded with a part with significant thermal load, as in the case of a printed wired board comprised of a tuner of the high frequency device for the TV receiver and the IF circuit, the power falls short such that soldering defects tend to be produced.
Thus, there is raised such a problem that, due to the above-mentioned thermal energy loss or the lowered part cooling effect, reliability of the non-heat-resistant parts tend to be lost or the soldering quality tends to be lowered to render it necessary to execute additional soldering.
It is therefore an object of the present invention to provide a soldering method and apparatus in which the hot air may be prevented from being directed to the part setting surface to reduce the heat energy loss without detracting from the circuit quality by soldering.
In one aspect, the present invention provides a soldering apparatus in which, for electrically connecting a non-heat-resistant part loaded on a substrate, a part soldering surface side of the substrate is heated by a re-flow unit. The soldering apparatus includes a re-flow panel of the re-flow unit having holes for ejecting a hot wind towards a soldering surface of the substrate, and a tight contact cover intimately contacting the re-flow panel except a portion thereof facing the substrate to be soldered.
In another aspect, the present invention provides a soldering method in which a solder is coated on a substrate, the substrate is inverted upside down, a non-heat-resistant part is loaded on the substrate and a soldering surface for the part of the substrate is heated by a re-flow unit, in which the method includes using a re-flow panel of the re-flow unit having holes through which a hot air is ejected towards the soldering surface of the substrate, and arranging a tight contact cover intimately contacting the re-flow panel except a portion thereof facing the substrate to be soldered to prohibit ejection of the hot wind through the holes.
According to the present invention, the holes in the portion of re-flow panel of the re-flow unit, other than the panel portion facing the substrate to be soldered, are tightly closed by the tight contact cover. So, the holes in the portion of the re-flow panel not facing the substrate, that is the unused portion, are closed, such that the hot wind not contributing to the heating of the part soldering surface of the substrate is not ejected from the re-flow panel.
Since there is no risk of the hot wind turning around to the part setting surface of the substrate, the loaded part is not heated by the hot wind to prevent the part from being affected in reliability. On the other hand, the thermal energy loss is diminished to improve the substrate heating efficiency by the re-flow panel. There is no risk of the occurrence of power shortage even if the printed wired board P is to be subjected to a high thermal load as in case the printed wired board is comprised of the tuner circuit of the high frequency device for TV receiver and an IF circuit. Thus, the part soldering surface of the printed wired board may be heated sufficiently to assure reliable soldering.
So, according to the soldering method and apparatus according to the present invention, the hot wind may be prevented from turning around to the part setting surface to suppress thermal energy loss without detracting from the circuit quality.